Agriculture Reference
In-Depth Information
Chapter 2
Impact of Extreme Events on Salt-Tolerant
Forest Species of Andaman and Nicobar
Islands (India)
Alok Saxena, P. Ragavan and Mani Saxena
1 Introduction
Andaman and Nicobar Islands situated in the Bay of Bengal off the eastern coast of
India (Fig.
2.1
) are endowed with very dense forest exhibiting rich diversity of plant
species. Luxuriant mangroves constitute one of the most important forest types that
exist in these islands. Mangroves are the salt-tolerant plants that are found mainly in
the tropical and sub-tropical intertidal regions of the world (www.mangroveindia.org).
They are defined as tree or bushes growing between the level of high water of spring
tide and level close to but above mean sea level (Macnae
1968
) or type of coastal woody
vegetation that fringes muddy saline shores and estuaries in tropical and sub-tropical
regions (Blasco et al.
1975
). Duke (
1992
) has defined a mangrove as “a tree, shrub,
palm or ground fern, generally exceeding one-half metre in height, and which normally
grows above mean sea level in the intertidal zone of marine coastal environment, or
estuarine margins”. A term often used while describing mangroves is 'mangal'. Macnae
(
1968
) suggested using the term 'mangal' to refer the mangrove ecosystem and the term
'mangrove' for referring the individual plant species. The mangrove forest ecosystem
comprises the intertidal flora and fauna in the tropics and sub-tropics and dominated
by evergreen sclerophyllous broad-leaved trees with stilt roots or pneumatophores and
viviparous seedlings (UNESCO
1973
).
There have been different estimates on global distribution of mangroves. Ac-
cording to McGill (
1959
), mangroves cover approximately 75 % of the World's
tropical coastline between 25° N and 25° S latitude. There have been different esti-
mates of area under mangroves in the world varying from 10 million ha to 24 mil-
lion ha. It is estimated at 16.2 million ha by Saenger et al. (
1983
), 10 million ha by
